Abstract:

A process for manufacturing an elastomeric tire component includes the
steps of a) preparing an elongated element including a cross-linkable
elastomeric material by feeding it to an extruding device having a
plurality of units, each having a respective thermal inertia, and b)
delivering the elongated element onto a building support, and further
includes at least one non-productive step of c) submitting at least one
of the units of the extruding device to a thermal transition selected
from heating or cooling, substantially reducing the risk of scorching
during the thermal transition from and to the non-productive step ranking
the units according to their thermal inertia and heating the units
starting with the top-ranked unit sequentially to the bottom-ranked unit
to reach the respective working temperature or cooling the units starting
from the maximum working temperature unit sequentially to the minimum
working temperature unit to reach the respective non-working temperature.

Claims:

1-34. (canceled)

35. A process for manufacturing an elastomeric tire component comprising
the steps of:a) preparing an elongated element comprising a
cross-linkable elastomeric material, by the steps comprising:a1) feeding
the cross-linkable elastomeric material to an extruding device comprising
a plurality of units; anda2) extruding the cross-linkable elastomeric
material by means of said extruding device so as to form said elongated
element,each of said units having a respective working temperature,each
of said units having a respective non-working temperature lower than said
working temperature, andeach of said units having a respective thermal
inertia, said units being ranked according to their thermal inertias so
as to have at least one top-ranked unit and at least one bottom-ranked
unit;b) delivering said elongated element onto a building support
rotatably moving about a geometrical rotation axis thereof, so that the
elongated element is circumferentially applied on the support; andc)
submitting at least one of the units of the extruding device to a thermal
transition selected from heating or cooling, wherein said thermal
transition is carried out by:c1) heating said at least one unit starting
from the top-ranked unit sequentially to the bottom-ranked unit to reach
the respective working temperature; or byc2) cooling said at least one
unit starting from the unit having the maximum working temperature
sequentially to the unit having the minimum working temperature to reach
the respective non-working temperature.

36. The process according to claim 35, wherein said units of the extruding
device comprise at least one housing, at least one member for moving the
elastomeric material within said housing and at least one shaping die.

37. The process according to claim 36, wherein said member for moving the
elastomeric material is selected from the group of a screw rotatably
mounted in said at least one housing and a piston slidably mounted in
said at least one housing.

38. The process according to claim 36, wherein said units of the extruding
device further comprise at least one nozzle.

39. The process according to claim 36, wherein said units of the extruding
device further comprising a gear pump.

40. The process according to claim 36, wherein said at least one housing
has a working temperature of 50.degree. C. to 120.degree. C.

41. The process according to claim 40, wherein said at least one housing
has a working temperature of 70.degree. C. to 90.degree. C.

42. The process according to claim 36, wherein said at least one member
for moving the elastomeric material has a working temperature of
20.degree. C. to 120.degree. C.

43. The process according to claim 42, wherein said at least one member
for moving the elastomeric material has a working temperature of
60.degree. C. to about 100.degree. C.

44. The process according to claim 36, wherein said at least one shaping
die has a working temperature of 80.degree. C. to 130.degree. C.

45. The process according to claim 44, wherein said at least one shaping
die has a working temperature of 90.degree. C. to 120.degree. C.

46. The process according to claim 38, wherein said at least one nozzle
has a working temperature of 70.degree. C. to 120.degree. C.

47. The process according to claim 46, wherein said at least one nozzle
has a working temperature of 80.degree. C. to 120.degree. C.

48. The process according to claim 39, wherein said at least one gear pump
has a working temperature of 70.degree. C. to 120.degree. C.

49. The process according to claim 48, wherein said at least one gear pump
has a working temperature of 80.degree. C. to 110.degree. C.

50. The process according to claim 35, further comprising the step of:d)
checking in real-time the actual temperature, the working temperature,
the non-working temperature and the difference between said actual
temperature and said working temperature of each of said units.

51. The process according to claim 50, wherein said checking step is
carried out by means of a temperature control system operatively
connected to the extruding device.

52. The process according to claim 51, wherein said temperature control
system comprises at least a sensor on a body of each unit.

53. The process according to claim 51, wherein said temperature control
system is provided with channels wherein a heat exchange fluid is
circulated.

54. The process according to claim 53, wherein said heat exchange fluid is
selected from pressurised water or oil.

55. The process according to claim 35, wherein said cross-linkable
elastomeric material has a maximum stay time, in each of said plurality
of units, 20% to 99% of the scorch time of said cross-linkable
elastomeric material at the actual temperature of the unit.

56. The process according to claim 55, wherein said cross-linkable
elastomeric material has a maximum stay time, in each of said plurality
of units, of 20% to 50% of the scorch time of said cross-linkable
elastomeric material at the actual temperature of the unit.

57. The process according to claim 36, wherein the top-ranked unit of the
extruding device is said housing thereof.

58. The process according to claim 36, wherein the bottom-ranked unit of
the extruding device is said shaping die thereof.

59. The process according to claim 39, wherein said units, as ranked in
decreasing order from the top-ranked unit to the bottom-ranked unit,
comprise: said at least one housing, said at least one member for moving
the elastomeric material within said at least one housing, said at least
one gear pump and said at least one shaping die.

60. The process according to claim 35, wherein the heating time of each of
said plurality of units differs from the heating time of the remaining
units of said plurality by an amount which is lower than or equal to 60
minutes.

61. The process according to claim 60, wherein the heating time of each of
said plurality of units differs from the heating time of the remaining
units of said plurality by an amount which is lower than or equal to 30
minutes.

62. The process according to claim 35, wherein the heating step of each
predetermined unit different from said top-ranked unit starts when the
actual temperature of the preceding unit of higher rank reaches a value
which is 20.degree. C. to 30.degree. C. lower than the working
temperature of said preceding unit.

63. The process according to claim 35, wherein the heating of said
plurality of units is carried out so that the units reach their
respective working temperature in less than 10 minutes.

64. The process according to claim 35, wherein cooling is managed by
activating a timer that is started for each of the units of the extruding
device from the time at which the extruding device has been stopped for
starting said cooling thermal transition.

65. The process according to claim 35, wherein the cooling of a
predetermined unit different from said unit having the maximum working
temperature starts when the stay time of the elastomeric material in said
unit reaches a threshold value of 20% to 99% of the scorch time of the
elastomeric material at said maximum working temperature.

66. The process according to claim 35, wherein the non-working temperature
of said unit having the maximum working temperature is 50.degree. C. to
80.degree. C.

67. The process according to claim 39, wherein said units, as ranked in
decreasing order from the unit having the maximum working temperature to
the unit having the minimum working temperature comprise: said at least
one shaping die, said at least one gear pump, said at least one member
for moving the elastomeric material within said at least one housing, and
said at least one housing.

68. The process according to claim 35, further comprising the steps
of:cooling said unit until having the maximum working temperature at its
non-working temperature; andmaintaining all the remaining units at their
respective working temperatures for a time period of 10 to 40 minutes
before sequentially cooling said remaining units.

Description:

[0001]The invention relates to a process for manufacturing elastomeric
tire components and more particularly tire components for motorvehicles.

[0002]Generally speaking, a tire for motorvehicles comprises a carcass
structure made up of one or more carcass plies of a substantially
toroidal shape and having their axially opposite side edges in engagement
with respective annular reinforcing elements usually referred to as "bead
cores", a tread band made of an elastomeric material at a radially outer
position with respect to said carcass structure, a belt structure
interposed between said carcass structure and said tread band and a pair
of axially opposite sidewalls on said carcass structure, each of which
covers a side portion of the tire radially extending between a so-called
shoulder region of the tread band and a so-called bead located at the
respective bead core.

[0003]It should be specified herein that in the present description and in
the subsequent claims, the term "elastomeric material" is used to
indicate a composition comprising at least one elastomeric polymer and at
least one reinforcing filler. Typically, such a composition also
comprises additives such as, for example, a vulcanizing agent and/or a
plasticizer. Thanks to the presence of the vulcanizing agent, such a
material may be vulcanized by heating, so as to form the end product.

[0004]In the field of tire manufacture, it has been proposed to form
elastomeric tire components by laying a continuous elongated element of a
suitable elastomeric material onto a substantially cylindrical or
toroidal support rotatable about its rotation axis. Such a continuous
elongated element generally has a reduced size as compared with that of
the final component to be obtained and is arranged on the rotatable
support so as to form a plurality of consecutive coils arranged side by
side and/or in overlapped relationship with one another.

[0005]It should be specified herein that in the present description and in
the subsequent claims, the term "elastomeric tire component" is used to
indicate all those components of the final tire, or parts thereof, which
are constituted by an elastomeric material.

[0006]Non limitative examples of elastomeric tire components according to
this definition are: the tread band; the sidewalls; the so-called liner,
that is a thin layer of elastomeric material that, once vulcanization has
been completed, will be airtight so as to ensure maintenance in use of
the tire's inflating pressure; the so-called under-liner, interposed
between the liner and the carcass plies; the under-belt inserts; the
filling inserts of the annular reinforcing structures; the sidewall
inserts of the so-called run-flat tires; the abrasion-resistant inserts
externally applied close to one of the tire bead elements; or parts of
any of these exemplary components.

[0007]In particular, when, as an example, the sidewalls and/or the tread
band are realized in two or more distinct parts, each made of a specific
elastomeric material, the term "elastomeric tire component" indicates
each of the aforesaid parts of the sidewalls and/or of the tread band.

[0008]International patent applications WO 00/35666 and WO 01/36185, in
the name of the present Applicant, teach that some of the tire components
can be obtained by delivering an elongated element from an extruder and
by suitably depositing this element on a support bearing the green tire
being manufactured, said support being rotated about its own axis and
moved with respect to the extruder by a robotized arm for obtaining a
transversal deposition of the elongated element to form a plurality of
circumferentially axially adjoined and/or radially overlapped coils that
give rise to the tire component. The orientation and mutual-overlapping
parameters of said coils are suitably managed so as to control the
thickness of each a elastomeric tire component being made, based on a
predetermined deposition scheme preset on an electronic computer.

[0009]Known from document GB 1,048,241 is a machine for laying down a
layer of elastomeric material of varying thickness on a tire carcass and
comprising a feeding head to apply a ribbon of elastomeric material to
the carcass, means for setting the carcass in rotation about its axis for
winding of a plurality of coils thereon when the carcass rotates with
respect to the feeding head, means for moving the feeding head
transversely of the carcass, from one side to the other of the
circumferential median plane of the carcass, and means for automatically
varying the transverse-movement amount for each winding revolution so as
to vary the overlapping degree of the contiguous coils and consequently
thickness of the layer formed on the carcass. In an appropriate version
for making new tires, during formation of the tread band the carcass is
mounted on a building drum and has a cylindrical right conformation.

[0010]EP 1 211 050 describes a method for extruding a tire rubber material
by a positive displacement extruding system including as seen from an
upstream side of the tire rubber, a screw extruder unit, a gear pump unit
and an extrusion head unit with an extrusion nozzle, which are connected
in series with each other. While the tire rubber is caused to flow
through the extruding system, the temperature of the rubber material is
measured and controlled to be within a predetermined temperature range.

[0011]EP 492,425 describes an extrusion system and a method for extruding
strips of rubber compounds which are uniformly heated and mixed in an
extruder. A control system regulates the speed of the extruder to provide
a near constant pressure at the entrance port of the gear pump to
precisely regulate the rate of extrusion of the compound from the
extrusion head. The temperature of the rubber compound is maintained
within a predetermined temperature range less than 100° C.
Temperatures and pressures are said to be measured at the various other
positions in the system as inputs for algorithms which are designed to
induce changes in the speed of feed mixer during start-up, shutdown and
steady state operations, to maintain the desired pressures, feed rates
and temperatures throughout the entire system.

[0012]U.S. Pat. No. 6,468,067 discloses a composite extruding apparatus of
rubber and a method of extruding unvulcanized rubber. The apparatus has a
reduced screw length, whereby the material residue is reduced, and the
temperature control is facilitated to prevent rubber scorching. The
temperature control is said to be effected by an ordinary method.

[0013]The Applicant observed that the methods and apparatuses of the prior
art for manufacturing elastomeric tire components have some drawbacks.

[0014]In particular, the industrial process can imply transitions from
productive to non-productive steps and vice-versa. In other words, the
production can be interrupted for various reasons, for example, problems
in or specific requests from a subsequent station of the manufacturing
plant, or a failure of a part of the extruder.

[0015]One of the problems faced when extruding elastomeric tire components
including a cross-linkable elastomeric material is connected with the
temperature control of the extruder. Excessive and/or unduly prolonged
heating can cause the premature vulcanization, otherwise known as
"scorch", of the cross-linkable elastomeric material. On the other side,
a temperature such to provide the elastomeric material with a fluidity
suitable for the workability should be maintained.

[0016]The Applicant experienced the necessity of timely and efficiently
managing the temperature of the different parts of an extruding device
during these transitions, taking into account, e.g., the following
aspects: [0017]the extruding device comprises units which differ in
terms of mass, thermal inertia and working temperature; [0018]emptying
the extruding device by totally discharging the elastomeric material
during the pause is not only expensive and time-consuming, but also
difficult to achieve, and residues of material can remain inside the
extruding device for a long time and consequently alter the quality of
subsequent extruded components; [0019]the material to be worked-up is
thermal sensitive.

[0020]In the production contexts of manufacturing elastomeric tire
components to which the present invention is addressed, the Applicant has
become aware of the fact that traditional methods, in which said
non-productive step lasts for a prolonged period of time during which the
elastomeric material remain at high temperatures, tend to produce a
material that is subjected to the aforementioned undesired premature
vulcanization ("scorching" phenomenon), generating a low-quality
elastomeric material, not having the requested physical-mechanical
properties.

[0021]In addition, due to said different characteristics of each of the
units of the extruding device, the Applicant further experienced that,
during said non-productive steps, it was difficult to manage the
transition of each unit from a non-working temperature to a working
temperature or vice-versa, as herein below defined, avoiding scorching
phenomena and obtaining at the same time the best results in terms of
time and energy consumption.

[0022]In accordance with the present invention, in dealing with the above
discussed problems, the Applicant has considered the possibility of
achieving substantially improvements in terms of production flexibility
and quality of the product by manufacturing an elastomeric tire component
by a process which manages in a specific way the thermal transitions from
and to said non-productive steps.

[0023]In more detail, it is an object of the present invention to provide
a process for manufacturing an elastomeric tire component comprising the
productive steps of:

a) preparing an elongated element including a cross-linkable elastomeric
material, andb) delivering said elongated element onto a building support
rotatably moving about a geometrical rotation axis thereof, so that the
elongated element is circumferentially applied on the support;the
preparing step a) comprising:a1) feeding the cross-linkable elastomeric
material to an extruding device comprising a plurality of units;a2)
extruding the cross-linkable elastomeric material by means of said
extruding device so as to form said elongated element;each of said units
having a respective working temperature;each of said units having a
respective non-working temperature lower than said working
temperature;each of said units having a respective thermal inertia, said
units being ranked according to their thermal inertias so as to have at
least one top-ranked unit and at least one bottom-ranked unit;said
process further comprising at least one non-productive step ofc)
submitting at least one of the units of the extruding device to a thermal
transition,wherein said thermal transition is carried out by [0024]c1)
heating said at least one unit starting from the top-ranked unit
sequentially to the bottom-ranked unit to reach the respective working
temperature; or by [0025]c2) cooling said at least one unit starting from
the unit having the maximum working temperature sequentially to the unit
having the minimum working temperature to reach the respective
non-working temperature.

[0026]Thermal inertia (I) is herein defined as the tendency of a material
to resist changes in temperature and can be expressed as follows:

I=(κρc)1/2

wherein k is the thermal conductivity, ρ is the bulk density of the
material; and c is the specific heat capacity per unit mass, i.e.
J/cm2sec1/2C.° (Joule on per square centimeter per
square root second per centigrade).

[0027]Working temperature of the units of the extruding device is herein
defined as the temperature at which each unit of the extruding device is
maintained during the extrusion operations of the process for
manufacturing the thermo-vulcanizable elastomeric material; that means,
that, at temperature values lower than said working temperature, the
extrusion process is in the non-productive step.

[0028]Non-working temperature of the units of the extruding device is
herein defined as a temperature lower than the working temperature and
which allows to avoid scorching phenomena of the cross-linkable
elastomeric material residing in the unit for a predetermined stay time.
Said non-working temperature can correspond to the room temperature in
case of a shut-down of the extruding device. Said non-working temperature
can also correspond to a temperature higher than the room temperature
during a non-productive step of the process in which the extruding device
is stand-by such as, for example, in case of an emergency.

[0029]The stay time for each unit, as herein defined, is the time that a
portion of the elastomeric material spends in said unit. On the other
hand, the scorch time is herein defined as the safety margin of time that
a rubber compound can be worked at a given temperature before
vulcanization begins. Scorch time can be measured with an oscillating
disc rheometer (ODR) according to ASTM D4084-95 and is the time necessary
to increase the torque value of two units (TS2 or Mooney Scorch).

[0030]The process for manufacturing an elastomeric component of the
present invention comprises at least one non-productive step, being
herein defined as a step in which the manufacturing process is in
stand-by, i.e. the polymeric material is not delivered/advanced through
the extruding device. Examples of non-productive steps are the extruding
device start-up, emergencies and pauses.

[0031]According to the invention, said at least one non-productive step of
submitting the units of the extruding device to a thermal transition
selected from heating or cooling is carried out by: [0032]heating said
at least one unit starting from the top-ranked unit sequentially to the
bottom-ranked unit to reach the respective working temperature; or by
[0033]cooling said at least one unit starting from the unit having the
maximum working temperature sequentially to the unit having the minimum
working temperature to reach the respective non-working temperature.

[0034]Sequentially" means that a unit can get involved in the thermal
transition when the previously involved unit is still under thermal
transition.

[0035]During said non-productive step, entailing cooling of the units, due
to the high temperatures present within said units of the extruding
device, and due to the fact that said extruding device has been stopped
thereby trapping therein a certain amount of elastomeric material, there
is the risk that the latter may undergo to scorching phenomena when a
critical threshold value of the stay time is surpassed.

[0036]If these phenomena occur a low-quality elastomeric tire component
without the requested physical-mechanical properties could be generated.
In addition, a prevulcanization of the elastomeric material would imply
the need of removing all the traces of scorched material from the
extruding equipment before starting a new production cycle, such removing
being time-consuming and in some cases not fully accomplishable.

[0037]The Applicant has surprisingly found that the process of the present
invention allows to substantially reduce the risk of scorching phenomena,
due to the fact that said cross-linkable elastomeric material remains in
at least one of the units of the extruding device for limited controlled
periods of time and/or at controlled temperature.

[0038]Still in accordance with the present invention, the Applicant has
found that it is possible to overcome the constraints of the processes of
the known art in terms of time and energy consumption during the
aforementioned cooling thermal transitions thanks to the fact that it is
possible to maintain most of the units having a lower working
temperatures at their respective working temperature, while only those
having a higher working temperature (with a higher risk of scorching) are
cooled to their non-working temperatures.

[0039]Said elongated element including a cross-linkable elastomeric
material used in the process of the present invention preferably has a
flattened cross-section, such as for example rectangular, elliptical or
lenticular, which is greatly reduced as compared with the cross-section
of the elastomeric component that is wished to be made. By way of non
limitative example, said elongated element may have a width included in
the range of from 3 millimeters to 15 millimeters, and a thickness
included in the range of from 0.5 millimeters to 2 millimeters.

[0040]The elongated element used in the process of the present invention
can be delivered onto a building support rotatably moving about a
geometrical rotation axis thereof, so that the elongated element is
circumferentially applied on the support.

[0041]Preferably, the building support has an outer surface substantially
mating in shape to the inner configuration of the tire to be formed. More
preferably, said building support is a substantially rigid toroidal
support. In an alternative embodiment, the building support may have a
substantially cylindrical outer surface.

[0042]The extruding device used in the process of the present invention is
generally positioned close to the building support so as to facilitate
the delivering operations of the elongated element onto the building
support itself.

[0043]The extruding device used in the process of the present invention
may be a conventional extruder or injector equipment and comprises a
plurality of units.

[0044]Preferably, said units include: at least one housing, at least one
member for moving the elastomeric material within said housing and at
least one shaping die.

[0045]Preferably, said at least one member for moving the elastomeric
material is selected from the group consisting of a screw rotatably
mounted in said at least one housing and a piston slidably mounted in
said at least one housing.

[0046]Preferably, the extruding device further includes at least one
nozzle. More in particular, said extruding device is preferably provided
with a so-called outlet "die" for shaping the elastomeric material being
worked at an orifice conveniently shaped and sized depending on the
geometric and dimensional features to be given to the product itself.

[0047]Preferably, the extruding device further includes a gear pump
operatively associated to said member for moving the elastomeric material
to realize a positive-displacement extruding device. The gear pump
increases the elastomeric-material pressure until bringing it to values
included in the range of from about 200 and about 650 bars, preferably to
about 400 bars, said elastomeric material being finally extruded through
said die.

[0048]The extrusion screw and the gear pump are each preferably driven by
different power units, although said power units can be also replaced by
a single power unit.

[0049]Preferably, said at least one housing of the extruding device has a
working temperature within the range of from 50° C. to 120°
C., more preferably from 70° C. to 90° C.

[0050]Preferably, said at least one member of the extruding device for
moving the elastomeric material has a working temperature within the
range of from 20° C. to 120° C., more preferably from
60° C. to 100° C.

[0051]Preferably, said at least one shaping die of the extruding device
has a working temperature within the range of from 80° C. to
130° C., more preferably from 90° C. to 120° C.

[0052]Preferably, said at least one nozzle of the extruding device has a
working temperature within the range of from 70° C. to 120°
C., more preferably from 80° C. to 120° C.

[0053]Preferably, said at least one gear pump of the extruding device has
a working temperature within the range of from 70° C. to
120° C., more preferably from 80° C. to 110° C.

[0054]The above mentioned preferred temperature ranges are related to the
average compounds viscosity levels and scorching conditions. The
temperature level optimization should lead to a maximization of compounds
fluidity (higher temperature means lower extrusion pressure) minimizing
the scorch risk (lower temperature means less scorch tendency). The
indicated temperature ranges encompass the viscosity and scorching
conditions used in tire compounds.

[0055]For the purposes of the present description and of the claims which
follow, except where otherwise indicated, all numerical values expressing
parameters such as amounts, temperatures, percentages, and so forth, are
to be understood as being modified in all instances by the term "about".
Also, all ranges include any combination of the maximum and minimum
points disclosed and include any intermediate ranges therein, which may
or may not be specifically enumerated herein.

[0056]In a preferred embodiment, the process of the present invention
further comprises the step of

d) checking in real-time the actual temperature, the working temperature,
the non-working temperature and the difference between said actual
temperature and said working temperature of each of the units of the
extruding device.

[0057]Preferably, said checking step is carried out by means of a
temperature control system operatively connected to the extruding device.

[0058]Still more preferably, the temperature control system comprises at
least a sensor on a body of each unit.

[0059]In a preferred embodiment, the temperature control system is
provided with channels wherein a heat exchange fluid circulates. More
preferably, said heat exchange fluid is selected from pressurised water
or oil.

[0060]Preferably, said heat exchange fluid has a maximum pressure
comprised in the range of from 6 to 9 bar and, more preferably, of 7 bar.

[0061]In the process of the present invention, said cross-linkable
elastomeric material has a stay time that is equal to or lower than the
scorch time, in each units.

[0062]Preferably, said cross-linkable elastomeric material has a stay
time, in each unit, ranging of from 20% to 99% of the scorch time of said
cross-linkable elastomeric material at the actual temperature of the
unit.

[0063]More preferably, said cross-linkable elastomeric material has a stay
time, in each unit, ranging of from 20% to 50% of the scorch time of said
cross-linkable elastomeric material at the actual temperature of the
unit.

[0064]In order to carry out the process of the invention, each of the
units of the extruding device is ranked according to its thermal inertia
so as to have at least one top-ranked unit and at least one bottom-ranked
unit; in addition, all the intermediate ranked units between said
top-ranked unit and said bottom-ranked unit are also preferably ranked in
a decreasing order.

[0065]According to a preferred embodiment of the process of the present
invention, the top-ranked unit is the housing, while the bottom-ranked
unit is the shaping die.

[0066]More preferably, said units, as ranked in decreasing order from the
top-ranked unit to the bottom-ranked unit according to their thermal
inertia, are: said at least one housing, said at least one member for
moving the elastomeric material within said at least one housing, said at
least one gear pump and said at least one shaping die.

[0067]According to a first aspect of the invention, all the units of the
extruding device or some of the same are submitted to a thermal
transition which is carried out by sequentially heating said units
starting from the top-ranked unit to the bottom-ranked unit to reach the
respective working temperature.

[0068]Thus, for example, during a non-productive step of the process which
comprises the start-up operations of the extruding device, all the units
are heated by raising the temperature of each unit from a preset
non-working temperature to a working temperature.

[0069]Preferably, the at least one housing of the extruding device is the
first unit to be submitted to said heating thermal transition during said
start-up non-productive step, being said housing the top-ranked unit,
while the other units are heated in sequence according to their different
thermal inertias, the bottom-ranked shaping die being the very last unit
to be submitted to the heating thermal transition.

[0070]Since each of the units needs a different time for passing from its
non-working temperature to its working temperature on account of its
specific thermal inertia, the heating step of the different units
preferably starts at different times during a given non-productive step,
so that the heating of the units last for different periods of time.

[0071]Preferably, the heating time of each of said plurality of units
differs from the heating time of the remaining units of said plurality of
an amount which is lower than or equal to 60 minutes, more preferably,
lower than or equal to 30 minute.

[0072]Preferably, the heating of each predetermined unit different from
said top-ranked unit starts when the actual temperature of the preceding
unit of higher rank reaches a value which is from 20° C. to
30° C. lower than the working temperature of said preceding unit;
more preferably, from 10° C. to 20° C. lower than the
working temperature of said preceding unit.

[0073]Still more preferably, the heating step of said plurality of units
is carried out so that the units reach their respective working
temperature in less than 10 minutes, more preferably substantially
simultaneously.

[0074]Within the framework of the present description and of the appended
claims, the expression: substantially simultaneously is used to indicate
that all the units reach their respective working temperatures at the
same time or that the period of time which lapses between the first unit
has reached its respective working temperature and the last unit has
reached its respective working temperature is lower than a predefined
value, such as, for example, lower than 5 minutes, preferably lower than
3 minutes.

[0075]According to a second aspect of the invention, all the units of the
extruding device or some of the same are submitted to a thermal
transition which is carried out by sequentially cooling said units.

[0076]Preferably, such a sequential cooling is managed by activating a
timer that is started for each of the units of the extruding device as
from the time at which the extruding device has been stopped for starting
said cooling thermal transition. Being activated said timer, it is
possible to check that the stay time of the elastomeric material, in each
unit, is always equal to or lower than the scorch time, measured by
Mooney Scorch as stated above.

[0077]Since each of the units needs a different time for passing from its
working temperature to its non-working temperature on account of its
specific stay time, the cooling step of the different units preferably
starts at different times during a given non-productive step, so that the
cooling of the units lasts for different periods of time.

[0078]Thus, for example, during a non-productive step of the process due
to an emergency or to a pause, all or some of the units of the extruding
device are sequentially cooled by first lowering the temperature of the
unit having the maximum working temperature from its preset working
temperature down to its non-working temperature. Then, the cooling of a
predetermined unit different from said unit having the maximum working
temperature starts when the stay time of the elastomeric material, in
said unit, reaches a threshold value comprised in the range of from 20%
to 99% of the scorch time of the elastomeric material at said maximum
working temperature.

[0079]Preferably, said at least one shaping die of the extruding device is
the first unit to be cooled during said non-productive steps, being the
shaping die the unit having the maximum working temperature, while the
other units are cooled in sequence according to the different stay time
of the elastomeric material in each of said units.

[0080]More preferably, during said cooling non-productive step, said
units, ranked in decreasing order from the unit having the maximum
working temperature to the unit having the minimum working temperature,
are: said at least one shaping die, said at least one gear pump, said at
least one member for moving the elastomeric material within said at least
one housing, and said at least one housing.

[0081]In a preferred embodiment, during said non-productive emergencies
and pauses steps, the non-working temperature of said unit having the
maximum working temperature is set within the range of from 50° C.
to 80° C., preferably from 60° C. to 70° C.

[0082]According to another preferred embodiment, the present invention
further comprises the steps of:

e) cooling said unit having the maximum working temperature at its
non-working temperature;f) maintaining all the remaining units at their
respective working temperatures for a time period comprised in the range
of from 10 to 40 minutes, more preferably for 20 minutes, before
sequentially cooling said remaining units.

[0083]After that period of time, a scorching process can occur in said
involved unit. That means that, if said emergencies and pauses would last
for a prolonged period of time, for example, for more than 20-40 minutes,
the temperatures of all the remaining units are decreased from their
working temperature to their non-working temperature.

[0084]Most advantageously, the process of the present invention allows to
manage in a proper way any temporary non-productive step carried out
after a productive step entailing the extrusion of the elastomeric
material, since the temperatures of the various units of the extruding
device are lowered to avoid any scorching phenomena of the elastomeric
material standing still in the extruding device.

[0085]Most advantageously, such a temperature management is carried out by
cooling in sequence the units as necessary, thereby saving energy and
reducing heating time once the pause is finished and the cooled unit(s)
of the extruding device should be heated again to reach (its) their
working temperature.

[0086]In a preferred embodiment of the process, such a heating may be
carried out in accordance with the procedures illustrated above.

[0087]The Applicant has surprisingly found that the process of the present
invention allows to reduce the risk that scorching phenomena, which are
observed in similar non-productive steps in extrusion processes known in
the art, may occur both during the start-up of the process and during
pauses of the same. This technical effect has been achieved
notwithstanding the various constraints in terms of thermal inertia, stay
time and energy consumption which affect the manufacturing equipment
available nowadays.

[0088]Further features and advantages will become more apparent from the
detailed description of a preferred, but not exclusive, embodiment of a
method and an apparatus for assembling tires for vehicle wheels, in
accordance with the present invention.

[0089]This description will be set out hereinafter with reference to the
accompanying drawings, given by way of non-limiting example, in which:

[0090]FIG. 1 is a diagrammatic perspective view of a robotized work
station for manufacturing an elastomeric tire component of a tire on a
substantially rigid toroidal support according to a preferred embodiment
of the present invention;

[0091]FIG. 2 is a schematic view of an extruding device used in the
process of the present invention;

[0092]FIG. 3 is a diagram showing the heating sequence during a start-up
non-productive step according to the process of the present invention;

[0093]FIG. 4 is a diagram showing the cooling sequence during a temporary
non-productive step according to the process of the present invention.

[0094]With reference to FIG. 1, a robotized work station intended to
manufacture an elastomeric tire component of a tire, for example the
tread band thereof, is generally indicated at 1.

[0095]The work station 1 is associated to a conventional manufacturing
plant for the production of pneumatic tires, or for carrying out part of
the working operations foreseen in the production cycle of the pneumatic
tires themselves, plant otherwise not illustrated being known per se.

[0096]The work station 1 comprises a robotized arm known per se, generally
indicated at 30 and preferably of the anthropomorphic type with seven
axes, intended to position a toroidal support 18 supporting a carcass
structure of the tire, an annular reinforcing structure and a belt
structure previously built in a known manner near a delivery position of
a continuous elongated element 20, made of a suitable elastomeric
material having a suitable size in cross-section, delivered by an
extruding device generally indicated at 19. The elastomeric material is
thus fed to the extruding device 19 to be extruded to form said elongated
element 20.

[0097]Preferably, the toroidal support 18 is provided with an outer
surface 18a substantially conforming in shape to the inner configuration
of the tire to be formed.

[0098]FIG. 2 schematically shows a preferred extruding device 19 used in
carrying out the process of the present invention.

[0100]Each of said units is characterized by a specific mass M and by a
specific working temperature T. Hence, the heating time of each unit
differ from that of the other units.

[0101]With reference to FIGS. 2-4, a first preferred embodiment of a
process for manufacturing an elastomeric tire component according to the
present invention will now be illustrated.

[0102]In a first non-productive step, the units 191-194 of the extruding
device 19 are submitted to a thermal transition by sequentially heating
the same starting from the top-ranked unit to the bottom-ranked unit to
reach the respective working temperature.

[0103]In the illustrated preferred embodiment, the top-ranked unit is the
housing unit 191, having a mass M1 and a working temperature T1. Thus,
the housing unit 191 is the first unit which is activated in the heating
step, due to the fact that this is the unit which needs the highest
heating time to reach its working temperature T1, which is for example
equal to 70-90° C., preferably about 85° C.

[0104]According to a preferred embodiment of the process of the invention,
the unit of the extruding device 19 having an immediately lower rank, in
this case constituted by the screw unit 192, is heated only when the
actual temperature of the housing unit 191 is about to reach the working
temperature T1 of the housing unit 191.

[0105]In an example, the screw unit 192 may be conveniently heated when
the actual temperature of the housing unit 191 of higher rank is about
20° C. lower than its working temperature T1.

[0106]Similarly, the gear pump unit 193 is heated only when the actual
temperature of the screw unit 192 is about to reach its working
temperature T2, which is for example equal to about 75° C., while
the shaping die unit 194 is heated only when the actual temperature of
the gear pump unit 193 is about to reach its working temperature T3 which
is for example equal to about 95° C.

[0107]In this example, the working temperature T4 of the shaping die unit
194 may be of about 100° C.

[0108]In an example, the gear pump unit 193 may be conveniently heated
when the actual temperature of the screw unit 192 of higher rank is about
30° C. lower than its working temperature T2, while the shaping
die unit 194 may be conveniently heated when the actual temperature of
the gear pump unit 193 of higher rank is about 30° C. lower than
its working temperature T3.

[0109]In this way, all the four units 191-194 of the extruding device 19
may advantageously reach their respective working temperatures T1, T2, T3
and T4 approximately at the same time, allowing each unit to remain for
the minimum possible time at its respective working temperature before
the elastomeric material contained in the extruding device 19 could be
extruded, thereby substantially reducing the risk that scorching problems
could occur.

[0110]Once the extruding device 19 and the related extrusion operation
carried out by the same reach their steady-state conditions, the
extrusion of the elastomeric material in the form of the continuous
elongated element 20 may take place so as to form the desired elastomeric
component of the tire onto the tire structures already formed on the
toroidal support 18.

[0111]More particularly, the elongated element 20 is delivered onto the
building toroidal support 18 rotatably moving about a geometrical
rotation axis thereof, so that the elongated element 20 may be
circumferentially applied on the toroidal support 18.

[0112]In the preferred embodiment illustrated, the rotary motion of the
toroidal support 18 for circumferential distribution thereon of the
elongated element 20 is carried out by the robotized arm 30 which
conveniently moves the building support 18 in front of the extruding
device 19.

[0113]During the manufacturing process and should any situation occur
along the production line upstream or downstream of the extruding device
19 which may trigger any intentional or accidental pause of the same, the
invention provides that a cooling sequence is activated in order to
prevent the risk that scorching phenomena of the elastomeric material
could occur.

[0114]For example, a pause of the extrusion process could occur due to a
feeding block of the elastomeric material or to a maintenance working
operation.

[0115]In such a case, the manufacturing process of the invention comprises
a non-productive step in which the units 191-194 of the extruding device
19 are submitted to a thermal transition by sequentially cooling the same
starting from the unit having the maximum working temperature to the unit
having the minimum working temperature to reach the respective
non-working temperature.

[0116]According to a preferred embodiment of the process of the invention
and as shown in FIG. 4, a timer is then started for each of the four
units 191-194 as from the time at which the extruding device has been
stopped, in order to check, in each unit, that the stay time of the
elastomeric material is always equal to or lower than the scorch time,
measured by Mooney Scorch as stated above.

[0117]The stay time of the unit having the maximum working temperature, in
this case constituted by the shaping die unit 194, is normally set up at
a value substantially equivalent to about 50% of the scorch time measured
at working temperature of the same unit 194, while the stay time of each
of the remaining units 192-194 normally has values higher than said stay
time value of unit 194, due to the fact that the temperatures in each of
said units are lower than the temperature in unit 194.

[0118]At the end of the maximum stay time allowable for unit 194 before
scorching at the working temperature thereof may take place, the
temperature of unit 194 is decreased to its preset non-working
temperature.

[0119]As an example, the non-working temperature of unit 194 may have a
value of approximately 65° C.

[0120]If the problem is solved during the maximum stay time of the
elastomeric material in the unit 194 or during its cooling to its
non-working temperature, the process of the invention advantageously
provides that only unit 194 is to be heated again to its respective
working temperatures because, during the stop, only said unit 194 was
brought to its non-working temperature while all the remaining units are
left at their respective working temperatures.

[0121]If, on the contrary, the problem is not solved during the cooling
step of the unit 194, the process of the invention provides--according to
a preferred embodiment thereof--that the unit of the extruding device 19
having the higher working temperature among the remaining units apart
unit 194, in this case constituted by the gear pump unit 193, is cooled
when the stay time of said unit 193 is at about 50% of the scorch time
measured at working temperature of the same unit 193.

[0122]Similarly, if necessary, the screw unit 192 and the housing unit 191
are cooled, in said order, only when the stay time of said units 192 and
191 are at about 40% of the scorch time, respectively, in said units 192
and 191.

[0123]In normal set up conditions, when unit 194 is at its non-working
temperature, the remaining units 193, 192, 191 can stay at their
respective working temperatures approximately for additional 30 minutes
in total, before it is necessary to also reduce their actual temperatures
to their respective non-working temperatures to avoid scorching problems.

[0124]The total time which elapses between the moment in which the
equipment finished the last extrusion of the elastomeric material and the
passage of all the units 193, 192, 191 from their respective working
temperatures to their respective non-working temperatures normally lasts
about 40 minutes; said time period normally allows to solve the problems
which usually occur in the production lines and which cause a stop of the
extrusion process.

[0125]If, on the contrary, the cause of the stop of the extrusion process
can not be eliminated in due time, all the units 193, 192, 191 pass from
their respective working temperatures to their respective non-working
temperatures.

[0126]If the cause of the stop of the extrusion process persists, an
additional period of time is allowed, before all the units are subjected
to an additional cooling step that definitively decreases their
temperatures from their respective non-working temperatures to the cold
equipment temperature, that is the temperature reached by the extruding
device and all the units included thereof when the extrusion process is
completely stopped.

[0127]In case it is possible to eliminate the cause of the stop of the
extrusion process during said additional period of time, the process
allows the units to reach again their respective working temperatures in
a time lower than the time needed in case the units reach said lower cold
equipment temperature value.

[0128]On the contrary, if it is not possible to eliminate the cause of the
stop of the extrusion process during said additional period of time, all
the units reach said cold equipment temperature, from which a process
involving a new heating step starts again, as the one described above
with reference to FIG. 3.